The present invention relates to thermal imaging systems. In particular, the present invention reduces "shading" problems which have been encountered in some types of thermal imaging systems.
Thermal imaging systems have been the subject of ever-increasing interest in recent years. These systems which provide images based upon invisible infrared radiation received from a scene, have found use in reconnaissance systems, in navigational systems for aiding navigation of vehicles under conditions of limited visibility, in diagnostic medical systems which aid physicians in detecting various forms of cancer, and in a variety of other applications.
One common type of thermal imaging system includes an objective lens, a moving scanner, an "imaging" or "detector" lens, and an infrared detector (or detector array), all of which are mounted in an optical housing. Radiation from the scene is received by the objective lens. The moving scanner scans the scene and the imaging lens images the thermal radiation from the scanner onto the detector. By moving the scanner, the detector effectively is scanned across a field of view, so that the electrical signals from the detector can be used to generate an image of the scene.
In thermal imaging systems of this type, it is general practice to provide an aperture stop near the objective lens. The purpose of this aperture stop is to provide for a constant amount of radiation from all points in the field of view.